Iodine/iodide leaching processes for the recovery of gold from gold-containing materials are well known to the art, and are described for example, in Applicant's U.S. patent application Ser. No. 598,706, to be issued as U.S. Pat. No. 4,557,759, incorporated herein by reference, and in U.S. Pat. Nos. 2,304,823 and 3,957,505.
When iodine and iodide attack an auriferous ore containing pyrite or other reducing materials, gold is solubilized as an iodide complex, either AuI.sub.2.sup.- or AuI.sub.4.sup.-, and pyrite or other reducing materials are oxidized by elemental iodine, forming iodide as one of the products. For the mining process to be economical, the lixiviant must be recycled; thus, any iodine which has been reduced must be restored to the solution in the oxidized (elemental) form, and the gold must be removed.
This combination of requirements, restoration of iodine and removal of gold, is difficult to accomplish inexpensively either simultaneously or sequentially. The difficulty arises from the fact that elemental iodine and the iodo-gold complex behave similarly in the presence of reducing agents, ion-exchange resins, and activated carbon. Thus, cementation of gold onto iron or zinc results in the solubilization of large amounts of these metals because iodine as well as gold effects their oxidation. Adsorption of gold onto an anion resin or activated carbon is inhibited by simultaneous adsorption of iodine onto available sites, and elemental iodine is quantitatively removed from the solution in the process.
The object of the present invention is to provide an economic process for recovering gold from an iodine-containing lixiviant in a one-step process in which gold and iodine are electrolytically reduced simultaneously with the oxidation of iodide. Iodine is produced at a rate sufficient to provide for a recycle leaching of gold. A further object of the invention is to prevent iron fouling of the electrolysis.